I. Field of the Invention
This invention relates to fuel gas ignition and combustion monitoring systems, and more particularly to a system and method which utilize an electronically monitored ignition and combustion monitoring device for controlling the operation of a gas fired appliance.
II. Background Art
Fuel gas is used in a wide range of gas fired appliances including ranges, stoves, gas refrigerators, barbecue pits, gas fired fireplaces, clothes dryers and water heaters. A conventional mechanism for igniting the fuel supplied to the gas fired appliances is a high voltage spark created by a spark generator. In spark ignition, two separated conductors have a voltage potential difference therebetween sufficient to induce a spark to jump the gap separating the two conductors. A third rod is engulfed in the flames of combustion and is used by the conductivity thereof to ascertain ongoing combustion. The conductivity of the air and third rod within the combustion envelope verifies that combustion is ongoing.
A problem known to spark generation equipment is the large draw of power required to make the spark jump the gap. This is particularly true if, by some happenstance, the gap size is increased between the two conductors. Additionally, the spark causes electromagnetic interference which tends to be a nuisance to radios, television sets, personal computers, and other electronic appliances in the area. In light of such a problem with spark ignition systems, it would be an advance in ignition systems for gas fired appliances to provide an ignition system that meets both conventional and developing telecommunication standards for electromagnetic interference omission.
Gas fired appliances are frequently controlled by microprocessors. Such microprocessors can be interfered with by spark generators. Additionally, the high voltages characteristics of spark generation can be deleterious to semiconductors in the control system of the appliance, as such high voltages can lead to the breakdown of semiconductor parts therein. Thus, the reliability of semiconductor components for controlling gas fired appliances may be jeopardized.
Another problem known to spark generators for the ignition of gas fired appliances is that the spark that is generated is consistent in both standard magnitude and size for an average environment of relative humidity. Consequently, in very high ambient relative humidity, the spark being generated may be insufficient to cause proper ignition of the fuel gas. Particulates in the air, accumulations of soot, and variations in altitude, in addition to the foregoing, can hinder spark generation and the ignition of the fuel gas.
An option to spark ignition for gas fired appliances is circuit ignition using a hot carbide surface, such as silicon carbide. Circuit ignitions are, however, typically more expensive than spark ignition systems. Carbides used for hot surface ignition of combustible fuel gases can withstand very high temperatures, have a high melting point, and are corrosion resistant. A difficulty with such hot surface ignition systems is the necessity of having to bond or otherwise weld the carbide to a metallic system that conducts electricity. This type of welding is necessary to electrically resistance heat the carbide, but is both expensive and difficult in that it requires very high temperatures to accomplish. Further, the carbide providing the hot surface ignition tends to be quite brittle and thus frangible and unreliable in physically non-fragile environments, such as is known to recreational vehicle appliances.
From the foregoing, it can be seen that it would be an advance in gas fired appliance ignition art to provide an ignition system that is inexpensive, does not cause electromagnetic interference with controllers of the gas fired appliance, and withstands heavy-duty use without breaking.
Gas fired appliances may have an ignition and combustion system that is regulated by a controller that causes the correct order, correct timing, and safety features thereof to be cooperating as subsystems of the appliance. Such modem gas fired appliances consist of a gas supply system, an ignition and combustion verification system, a safety cut-off valve to the gas supply system, and a heat extraction or heat exchange system. It is the goal of such controllers to provide transparent operation of the gas fired appliance to the user. By way of example, such a controller may control the combustion mix of air and fuel gas so that it is neither too lean nor too rich, but rather combusts most efficiently. Such a controller may regulate the operation of an electrically activated solenoid valve which opens and closes the gas flow to the appliance so that the right amount of gas at the right velocity is mixed into the combustion area or mixing space for combustion.
In the case of furnaces and other gas fired appliances requiring an air delivery system, a blower fan may also be operated by a controller. Should there ever be an extinguishment of combustion, a blower fan may be operated by the controller so as to purge the combustion area free of combustible fuel gas and thereby prevent a build up of same and a subsequent explosion. When the controller operates the blower fan following extinguishment of a flame, a safety timing period is provided between the receipt of the controller of a request of a thermostat to start opening the gas valve, and the subsequent opening of the gas valve supplying fuel gas to the combustion area. Thus, the controller may control the timing of the actual delivery and purging of the combustible fluid contents of the combustion area.
Another important function which may be controlled by a controller, and may also be accomplished by mechanical systems, is that of a sail switch which measures air flow to the combustion area. A sail switch is a mechanical switch that is switched on or off by the flow or non-flow of air. The switch signals the controller to turn off the supply of fuel gas if air flow to the combustion area has been terminated. By way of example, an obstruction in the air intake to the blower fan may cause a rich fuel gas mixture in the combustion area due to an absence of air coming through the air intake. A sail switch would prevent such a problem by giving an indication of air intake malfunctioning, which indication is acted on by the controller to prevent the fuel gas from flowing into the combustion chamber. Thus, gas is not combusted in the case where air is not being provided to the combustion area, or is not being provided so as to remove heat from the combustion chamber. The sail switch helps to indicate that air is flowing to reduce the heat of combustion, and thus prevent the burning up of heat exchanger components of the gas fired appliance.
In short, the sail switch is an anemometer to measure the amount of air that is being delivered to the combustion area. The sail switch, by its function of assuring that the appliance will not operate without a proper air flow to the combustion chamber, prevents a typical problem of air flow blockage or redirections of the air which may in turn cause the flames of redirection of the flames of combustion to be redirected to an area that is hazardous to the appliance.
While prior art sail switch techniques have been widely used with success, there is still a serious risk of human error when using such systems. The sail switches used on such gas fired furnaces are often prone to mechanical failure due to environmental conditions, and due to corrosion over time as the appliance ages. Thus, improper sail switch operation may occur. Accordingly, there is a need for a gas fired appliance that safely and accurately acknowledges a proper in take of air to the combustion area so as to assure that a flue is not blocked. The system and method of the present invention provide an effective solution to these problems which has not heretofore been fully appreciated or solved.
A controller for a gas fired appliance may also be in electrical communication with a limit switch or ECO. The ECO switch cuts off power so as to close the gas supply valve whenever certain critical areas of the appliance reach a maximum tolerable temperature. In the case of furnaces and other gas fired appliances having a blower fan to the combustion chamber, a timing relay is also operated in conjunction with the ECO so that there is a purging of the gas combustion area following the shut off of electrical power to the appliance.
An ignition control board or other appliance controller device, incorporates the foregoing functions of monitoring the ignition, combustion, and ongoing operation of a gas fired appliance. It would be an advance in art to provide a safe and reliable integrated ignition and combustion control system that overcomes foregoing problems while intercoordinating typical functions provided by a gas fired appliance.